Overview
ISO 534:2011 - "Paper and board - Determination of thickness, density and specific volume" defines standardized laboratory methods to measure the thickness (caliper) of paper and board and to calculate apparent density and specific volume from those measurements. It specifies two measurement approaches: single sheet thickness and bulking thickness (pack of sheets), the required instrumentation (dead‑weight precision micrometer), calibration/verification procedures, sampling and conditioning requirements, and result expression.
Key technical topics and requirements
- Two measurement methods
- Single sheet thickness: direct measurement of an individual sheet under a defined static load.
- Bulking thickness: measurement of a pack (normally ten sheets) and calculation of single‑sheet thickness from the pack reading (note: not suitable for board).
- Instrument and pressure
- Use a dead‑weight micrometer with parallel circular pressure faces; measurement pressure: (100 ± 10) kPa (the previously used 50 kPa option was removed).
- One pressure face diameter specified as (16.0 ± 0.5) mm; the contact region is nominally about 200 mm².
- Micrometer performance and calibration
- Verification/calibration in conditioning atmosphere as per Annex A.
- Performance limits (maximum permitted): indication error ±2.5 µm or ±0.5%, parallelism error 5 µm or 1%, repeatability 1.2 µm or 0.5% (greater of the two values applies).
- Sampling, preparation and measurement protocol
- Condition samples per ISO 187. Sample selection per ISO 186; grammage by ISO 536 when required.
- Single‑sheet test pieces: minimum 60 × 60 mm (max 100 × 100 mm for board); prepare ≥20 test pieces; record one reading per piece.
- Bulking test pieces: prefer 200 × 250 mm sheets, packs of 10 sheets, make ≥4 test pieces; measure at five positions per pack and divide mean by number of sheets.
- Results and calculations
- Thickness reported in micrometres to three significant figures.
- Apparent density d = g / δ (g = grammage in g/m²; δ = thickness in µm) - report density to two decimal places.
- Calculate standard deviation and 95% confidence interval as specified.
Practical applications and users
ISO 534:2011 is essential for:
- Paper and board manufacturers - process control, specification compliance.
- Quality assurance laboratories and testing services - repeatable caliper and density data.
- Converters, printers and packaging designers - assessing bulk, stiffness, compressibility and printability implications.
- R&D teams - material comparison and formulation development.
Using a common, documented method ensures comparable caliper, density and specific volume data across suppliers, labs and customers.
Related standards
- ISO 186 - Sampling to determine average quality
- ISO 187 - Standard atmosphere for conditioning and testing
- ISO 536 - Determination of grammage
- ISO 12625-3 - Use for tissue papers and tissue products (ISO 534 methods are not applicable to tissues)